JP5501559B2 - X-ray CT apparatus and image correction method - Google Patents

Description

  The present invention relates to an X-ray CT (Computed Tomography) apparatus and an image correction method, and in particular, an imaging means for imaging a tomogram of the head by a scan using X-rays, and correction for correcting the imaged tomogram. The present invention relates to an X-ray CT apparatus having means, and an image correction method for such an X-ray CT apparatus.

Since the tomographic image of the head imaged by the X-ray CT apparatus is deteriorated in image quality due to an X-ray beam hardening effect or a false image, image correction for image quality improvement is performed. A corrected image is used for image correction. The correction image is reconstructed by creating correction data from bone projection data (data) obtained by virtually projecting a bone image in the tomographic image of the head, and back-projecting the correction data (for example, Patent Document 1).
JP-A-10-75947 (paragraph number 0025-0031, FIG. 3-6)

  The quality of the corrected image depends on the corrected image. The corrected image is determined by correction data used for the reconstruction. For this reason, the quality of the image after correction depends on the correction data, but the image quality that can be realized by the conventional correction data is not always satisfactory.

  In particular, the tomographic image of the head has different beam hardening effects and false image states depending on whether the slice position is the posterior fossa level (level), the basal ganglia level, or the top of the head. It was difficult to correct the tomographic image so as to obtain high quality.

  Accordingly, an object of the present invention is to realize an X-ray CT apparatus capable of obtaining a high-quality head tomogram regardless of the slice position, and an image correction method for such an X-ray CT apparatus. .

  According to a first aspect of the present invention, there is provided an imaging unit that collects projection data of a subject by scanning using X-rays, and reconstructs a tomographic image of the head based on the projection data. Correction means that corrects the tomographic image using a correction image that is created by correcting projection data from the bone projection data obtained by virtually projecting the bone image in the tomographic image and backprojecting the correction data. An X-ray CT apparatus comprising gain setting means for determining a gain for generating the correction data from the bone projection data according to a bone thickness of the bone image in the tomographic image CT device.

  According to a second aspect of the invention for solving the problem, in the second aspect, the gain setting means sets the gain so that the degree of correction by the correction data is greater when the bone thickness is smaller than when the bone thickness is large. The X-ray CT apparatus according to the first aspect, characterized by being defined.

  According to a third aspect of the present invention for solving the problem, in the third aspect, the gain maintains a gain value that is a first correction level in a range from 0 to a first bone thickness setting value, and the first bone In the range from the thickness setting value to the second bone thickness setting value, the gain value that is the degree of the first correction continuously changes from the gain value that is the degree of the second correction smaller than that, The X-ray CT apparatus according to the second aspect is characterized in that the gain value which is the second correction level is maintained in a range exceeding the bone thickness setting value.

  The invention for solving the problem, in a fourth aspect, comprises gain correction means for correcting the gain according to an area ratio of the bone image of the inner region of the skull to the area of all the bone images in the tomographic image. The X-ray CT apparatus according to the first aspect, characterized in that:

  In a fifth aspect, the invention for solving the problem is characterized in that the inner region of the skull is an inner region that is more than k (> 1) times the bone thickness from the contour of the tomographic image. The X-ray CT apparatus according to the fourth aspect, which is characterized.

  According to a sixth aspect of the invention for solving the problem, in the sixth aspect, the correction is a correction that reduces the degree of correction by the correction data. X in the fourth aspect or the fifth aspect This is a line CT apparatus.

  The invention for solving the problem is, in a seventh aspect, according to the sixth aspect, wherein the amount of correction is small when the area ratio is small and large when the area ratio is large. X-ray CT apparatus.

  In an eighth aspect of the invention for solving the problem, in the eighth aspect, the correction amount maintains the first correction amount in the range from 0 to the first area ratio setting value, and the first area ratio setting value In the range up to the second area ratio set value, the first correction amount continuously changes from the second correction amount larger than that, and in the range exceeding the second area ratio set value, the second correction is made. The X-ray CT apparatus according to the seventh aspect, wherein the quantity is maintained.

  The invention for solving the problem, in the ninth aspect, creates correction data from bone projection data obtained by virtually projecting a bone image in a tomographic image of the head imaged by an X-ray CT apparatus, A method for correcting the tomographic image using a correction image reconstructed by backprojecting the correction data, wherein a gain for creating the correction data from the bone projection data is a bone of a bone image in the tomographic image This is an image correction method characterized by being determined according to the thickness.

  In a tenth aspect, the invention for solving the problem is characterized in that the gain is determined such that the degree of correction by the correction data is greater when the bone thickness is smaller than when the bone thickness is large. The image correction method according to the ninth aspect.

  In an eleventh aspect of the invention for solving the problem, in the eleventh aspect, the gain maintains a gain value that is a first correction degree in a range from 0 to a first bone thickness setting value, and the first bone In the range from the thickness setting value to the second bone thickness setting value, the gain value that is the degree of the first correction continuously changes from the gain value that is the degree of the second correction smaller than that, The image correction method according to the tenth aspect, wherein a gain value that is the second correction level is maintained in a range exceeding the bone thickness setting value.

  The invention for solving the problem, in a twelfth aspect, is characterized in that the gain is corrected according to an area ratio of a bone image of an inner region of the skull to an area of all bone images in the tomographic image. The image correction method according to the ninth aspect.

  In a thirteenth aspect, the invention for solving the problem is characterized in that the inner region of the skull is an inner region that is more than k (> 1) times the bone thickness from the contour of the tomographic image. The image correction method according to the twelfth aspect.

  According to a fourteenth aspect of the present invention for solving the problem, the image according to the twelfth aspect or the thirteenth aspect is characterized in that the correction is a correction that reduces the degree of correction by the correction data. This is a correction method.

  The invention for solving the problem, in a fifteenth aspect, is characterized in that the amount of correction is small when the area ratio is small and large when the area ratio is large. This is an image correction method.

  According to a sixteenth aspect of the invention for solving the problem, in the sixteenth aspect, the correction amount maintains the first correction amount in a range from 0 to the first area ratio setting value, and the first area ratio setting value In the range up to the second area ratio set value, the first correction amount continuously changes from the second correction amount larger than that, and in the range exceeding the second area ratio set value, the second correction is made. The image correction method according to the fifteenth aspect, wherein the amount is maintained.

  In the first aspect, imaging data for collecting projection data of a subject by scanning using X-rays, and reconstructing a tomographic image of the head based on the projection data, and a bone image in the tomographic image are virtually An X-ray CT apparatus having correction means for generating correction data from bone projection data obtained by projecting onto a bone, and correcting the tomographic image using a correction image reconstructed by back projecting the correction data, Since gain setting means for determining the gain for generating the correction data from the projection data according to the bone thickness of the bone image in the tomographic image is provided, a high-quality head tomographic image can be obtained regardless of the slice position. An X-ray CT apparatus can be realized.

  In a ninth aspect, correction data is created from bone projection data obtained by virtually projecting a bone image in a tomographic image of the head imaged by an X-ray CT apparatus, and the correction data is back-projected and reproduced. In the method of correcting the tomographic image using the configured correction image, the gain for creating the correction data from the bone projection data is determined according to the bone thickness of the bone image in the tomographic image. Regardless of this, it is possible to realize an image correction method capable of obtaining a high-quality head tomographic image.

  In the second or tenth aspect, the gain is determined such that the degree of correction by the correction data is greater when the bone thickness is smaller than when the bone thickness is large, so that the correction data can be optimized. .

  In the third or eleventh aspect, the gain maintains a gain value that is the first correction level in a range from 0 to the first bone thickness setting value, and exceeds the first bone thickness setting value. In the range up to the second bone thickness setting value, it continuously changes from a gain value that is the first correction level to a gain value that is the second correction level smaller than that, and the second bone thickness setting value is Since the gain value that is the degree of the second correction is maintained in the range exceeding the range, the gain can be optimized.

  In the fourth or twelfth aspect, since the gain is corrected according to the area ratio of the bone image of the inner region of the skull with respect to the area of all the bone images in the tomographic image, the gain can be further optimized. .

In the fifth or thirteenth aspect, since the inner region of the skull is an inner region that is more than k (> 1) times the bone thickness from the contour of the tomographic image, an effective area ratio can be obtained.
In the sixth or fourteenth aspect, since the correction is correction that reduces the degree of correction by the correction data, the gain can be corrected appropriately.

In the seventh or fifteenth aspect, since the amount of correction is small when the area ratio is small and large when the area ratio is large, the correction amount can be optimized.
In the eighth or sixteenth aspect, the correction amount maintains the first correction amount in the range from 0 to the first area ratio set value, exceeds the first area ratio set value, and the second amount. In the range up to the area ratio set value, it continuously changes from the first correction amount to the second correction amount larger than that, and in the range exceeding the second area ratio set value, the second correction amount is maintained. The correction amount can be further optimized.

  The best mode for carrying out the invention will be described below with reference to the drawings. Note that the present invention is not limited to the best mode for carrying out the invention. FIG. 1 shows a schematic configuration of an X-ray CT apparatus. This apparatus is an example of the best mode for carrying out the invention. An example of the best mode for carrying out the invention related to the X-ray CT apparatus is shown by the configuration of the apparatus. An example of the best mode for carrying out the invention relating to the image correction method is shown by the operation of this apparatus.

  The apparatus has a gantry 100, a table 200, and an operator console 300. The gantry 100 scans the subject 10 supported by the table 200 with the X-ray irradiation / detection device 110, collects projection data of a plurality of views, and inputs it to the operator console 300.

  The operator console 300 performs image reconstruction based on the projection data input from the gantry 100, corrects the reconstructed image, and displays the corrected image on (display) 302. Image reconstruction and correction are performed by a computer in the operator 300.

  The operator console 300 also controls the operation of the gantry 100 and the table 200. These controls are performed by a dedicated computer in the operator 300. Under the control of the operator console 300, the gantry 100 scans under a predetermined scanning condition, and the table 200 positions the subject 10 so that a predetermined part is scanned. Positioning is performed by adjusting the height of the top plate 202 and the horizontal movement distance of the cradle 204 on the top plate by a built-in position adjustment mechanism.

  An axial scan can be performed by scanning with the cradle 204 stopped. A cine scan can be performed by continuously performing the axial scan over a predetermined time. A helical scan can be performed by continuously performing a plurality of scans while continuously moving the cradle 204.

  The height adjustment of the top plate 202 is performed by swinging the support column 206 around the attachment portion to the base 208. The top plate 202 is displaced in the vertical direction and the horizontal direction by the swing of the column 206. The cradle 204 moves in the horizontal direction on the top plate 202 to cancel the horizontal displacement of the top plate 202. Depending on the scan conditions, the scan is performed with the gantry 100 tilted. The gantry 100 is tilted by a built-in tilt mechanism.

  As shown in FIG. 2, the table 200 may be of a type in which the top plate 202 moves up and down vertically with respect to the base 208. The top plate 202 is moved up and down by a built-in lifting mechanism. In this table 200, the horizontal movement of the top plate 202 accompanying the raising and lowering does not occur.

  FIG. 3 schematically shows the configuration of the X-ray irradiation / detection device 110. The X-ray irradiation / detection device 110 detects an X-ray 134 emitted from the focal point 132 of the X-ray tube 130 with an X-ray detector 150.

  The X-ray 134 is shaped by an aperture mechanism (not shown) and becomes a cone beam or fan beam X-ray. The X-ray detector 150 has an X-ray incident surface 152 that expands two-dimensionally corresponding to the spread of X-rays. The X-ray incident surface 152 is curved so as to constitute a part of a cylinder. The central axis of the cylinder passes through the focal point 132.

  The X-ray irradiation / detection device 110 rotates around a central axis passing through an imaging center, that is, an isocenter O. The central axis is parallel to the central axis of the partial cylinder formed by the X-ray detector 150.

  The direction of the center axis of rotation is the z direction, the direction connecting the isocenter O and the focal point 132 is the y direction, and the direction perpendicular to the z direction and the y direction is the x direction. These x, y, and z axes are three axes in a rotating coordinate system with the z axis as the central axis.

  FIG. 4 schematically shows a plan view of the X-ray incident surface 152 of the X-ray detector 150. The X-ray incident surface 152 has detection cells 154 arranged two-dimensionally in the x direction and the z direction. That is, the X-ray incident surface 152 is a two-dimensional array of detection cells 154. In the case of using fan beam X-rays, the X-ray incident surface 152 may be a one-dimensional array of detection cells 154.

  Each detection cell 154 constitutes a detection channel of the X-ray detector 150. Thereby, the X-ray detector 150 becomes a multi-channel X-ray detector. The detection cell 154 is configured by, for example, a combination of a scintillator and a photodiode.

  FIG. 5 shows a flow diagram of the operation of this apparatus when taking a tomographic image of the head. Imaging is performed under the control of the operator console 300. As shown in FIG. 5, the scan position is set in step 501. The scan position is set through the operator console 300 by the operator. Thereby, for example, the scan position of the head of the subject 10 is set with respect to the posterior fossa level, the basal ganglia level, the crown, or the like.

  In step 502, a scan protocol is set. The scan protocol is set through the operator console 300 by the operator. As a result, necessary imaging conditions such as the tube voltage and tube current of the X-ray tube, scan time, and image reconstruction conditions are set.

  In step 503, scanning is performed. The scan is performed by the gantry 100 and the table 200 under the control of the operator console 300, and projection data of the head having a predetermined number of views is collected at a predetermined scan position.

  In step 504, image reconstruction is performed. Image reconstruction is performed in the operator console 300, and a tomographic image of the head at a predetermined scan position is obtained. The image reconstruction is performed by, for example, a filtered back projection method. Note that the present invention is not limited to this, and image reconstruction may be performed by other appropriate methods.

  The gantry 100, the table 200, and the operator console 300 that perform scanning and image reconstruction in step 503 and step 504 are examples of imaging means in the present invention.

  In step 505, image correction is performed. Image correction is performed in the operator console 300. The operator console 300 is an example of correction means in the present invention. The image correction is for improving the image quality of the tomographic image of the head. Image correction will be described later.

  In step 506, an image is displayed. An image is displayed on the display 302. The displayed image is a corrected image. For this reason, a high-quality head tomogram is displayed on the display 302.

  FIG. 6 shows a flowchart of the image correction operation. This flowchart shows the operation of step 505 in FIG. 5 in an exploded manner into sub steps. All of these operations are performed by a computer in the operator console 300.

  As shown in FIG. 6, a bone image is extracted in sub-sub step 601. Bone image extraction is performed by extracting pixels having a CT value equal to or greater than a predetermined threshold from the tomographic image of the head. For example, 225 is used as the predetermined threshold.

  In sub-step 602, bone image projection is performed. The bone image projection is performed by virtually projecting the bone image in a plurality of view directions. The bone image projection is performed in accordance with the X-ray geometry of the X-ray irradiation / detection device 110. As a result, bone projection data of a plurality of views can be obtained as if a subject composed of only bones was scanned by the X-ray irradiation / detection device 110.

  In sub-step 603, bone thickness is calculated. The bone thickness is calculated by the following equation using the area S1 of the head section and the area S2 of the bone image in the section.

  As shown in FIG. 7, the bone thickness calculated by the above equation is a bone thickness r when it is assumed that the head section is circular and the bone thickness is uniform. The first term on the right side of the above formula represents the radius r1 of the circular cross section, and the second term represents the radius r2 of the inner surface of the skull.

  The area S1 of the head section is obtained as a product of the number of pixels having a CT value of, for example, 0 or more and the pixel size, and the area S2 of the bone image is the number of pixels having a CT value of, for example, 225 or more. Calculated as the product of size.

  In sub-step 604, the area ratio of the bone image is calculated. The area ratio of the bone image is the area ratio of the bone image in the inner region of the skull to the area of all bone images in the head section. As the inner region of the skull, for example, as shown in FIG. 8, an inner region R that is twice (2r) the bone thickness from the contour of the head cross section is employed. The inner region may be a region that is more than k (> = 1) times the bone thickness.

  In sub-step 605, a gain for creating correction data is set. The gain is also called IBO (Iterative Bone Option) gain. In the present embodiment, consider a case where correction data is calculated by a linear function using a single gain. The gain is set according to the bone thickness calculated in sub-step 603.

  The gain is set so that the degree of correction by the correction data is greater when the bone thickness is smaller than when the bone thickness is large. Thereby, for example, a large gain is set for a small bone thickness, and a small gain is set for a large bone thickness.

  FIG. 9 shows an example of the relationship between bone thickness and gain. As shown in FIG. 9, the gain maintains the first gain value G1 in the range of the bone thickness from 0 to the first bone thickness setting value T1, and exceeds the first bone thickness setting value T1. 2 continuously changes from the first gain value G1 to a smaller second gain value G2 in the range up to the bone thickness setting value T2, and the second bone thickness setting value T2 exceeds the second bone thickness setting value T2. The gain value G2 is maintained. The first bone thickness setting value T1 is, for example, 3.5 mm, and the second bone thickness setting value T2 is, for example, 7.5 mm.

  Such a gain characteristic is stored in the memory in the form of an equation or a numerical table, and is used for setting the gain. As a mathematical formula, for example, a linear formula is used. In addition, it may be a higher order expression of the second or higher order. The computer that sets the gain in sub-step 605 is an example of the gain setting means in the present invention.

  In sub-step 606, the gain is corrected. The gain is corrected according to the area ratio of the bone image calculated in sub-step 604. The correction amount is small when the area ratio is small, and the correction amount is large when the area ratio is large. The direction of correction is a direction in which the gain is reduced. As a result, the sign of the correction amount becomes negative.

  FIG. 10 shows an example of the relationship between the area ratio and the correction amount. As shown in FIG. 10, the correction amount maintains the first correction amount value −ΔG1 in the range where the area ratio is 0 to the first area ratio setting value R1, and the first area ratio setting value R1 is the same. In the range exceeding the second area ratio set value R2, the first correction amount value -ΔG1 continuously changes from the second correction amount value -ΔG2 having a larger absolute value to the second area ratio setting value R2. In a range exceeding the set value B, the second correction amount value −ΔG2 is maintained. The first area ratio set value R1 is, for example, 42%, and the second area ratio set value R2 is, for example, 52%.

  Such characteristics are stored in the memory in the form of mathematical formulas or numerical tables and are used for gain correction. As a mathematical formula, for example, a linear formula is used. In addition, it may be a higher order expression of the second or higher order. The computer that corrects the gain in sub-step 606 is an example of the gain correcting means in the present invention.

  In sub-step 607, correction data is created. The correction data is created by a linear function of gain using bone projection data. The gain used here is a gain that has been corrected according to the bone image area ratio. The corrected gain is applied to the multi-view bone projection data. As a result, correction data for a plurality of views is created.

  In sub-step 608, the corrected image is reconstructed. The reconstruction of the corrected image is performed based on the correction data. The reconstruction of the corrected image is performed by, for example, a filtered back projection method or the like, similar to the reconstruction of the head tomogram. Note that the present invention is not limited to this, and image reconstruction may be performed by other appropriate methods.

  In sub-step 609, image correction is performed. Image correction is performed by subtracting the corrected image from the original image, that is, the head tomogram. Subtraction of the corrected image from the head tomogram is performed between corresponding pixels.

  As shown in FIG. 9, the gain for creating correction data is large in the region where the bone thickness is small. By using a relatively large gain in this region and a relatively large degree of correction, the density resolution (LCD: Low Contrast Detectability) of a tomogram at a basal ganglia level with a relatively small bone thickness as shown in FIG. Can be increased.

  The gain is also relatively small in areas where the bone thickness is relatively large. By using a relatively small gain in this region and making the degree of correction relatively small, it is possible to suppress excessive beam hardening compensation for a tomogram of the parietal region having a relatively large bone thickness as shown in FIG. Can do.

  As shown in FIG. 10, the correction amount in the direction of decreasing the gain is large in the region where the area ratio is large. This is because, in the vicinity of the posterior skull fossa, there is a bone on the center side of the head, which causes the false image to stand out by correction. When the area ratio is large, the gain was obtained from the bone thickness It is corrected to be lower than the gain. Such correction has a significant effect on reducing the false image in the posterior fossa level tomogram as shown in FIG.

  Further, since the correction amount is small (= 0) in the region where the area ratio is small, the value obtained from the bone thickness is maintained as the gain. Therefore, the tomographic image LCD at the basal ganglia level is not deteriorated.

  The correction data may be a linear function of gain using the square value of the bone projection data, or a polynomial that is the sum of values obtained by multiplying the cubic value or the fourth power value of the bone projection data by a unique gain. . The gain by which the cube value, the fourth power value, or the like is multiplied is set to an appropriate value that can achieve the desired image quality.

It is a figure which shows the structure of the X-ray CT apparatus of an example of the best form for implementing invention. It is a figure which shows the structure of the X-ray CT apparatus of an example of the best form for implementing invention. It is a figure which shows the structure of a X-ray irradiation / detection apparatus. It is a figure which shows the structure of the X-ray entrance plane of an X-ray detector. It is a flowchart which shows operation | movement of the X-ray CT apparatus of an example of the best form for implementing invention. It is a flowchart which shows the detail of operation | movement of the X-ray CT apparatus of an example of the best form for implementing invention. It is a figure which shows the concept of bone thickness calculation. It is a figure which shows the concept of the inner side area | region of a skull. It is a figure which shows the relationship between bone thickness and a gain. It is a figure which shows the relationship between the area ratio of a bone, and a gain correction amount. It is a figure which shows a head tomogram with the photograph of a halftone. It is a figure which shows a head tomogram with the photograph of a halftone. It is a figure which shows a head tomogram with the photograph of a halftone.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10: Subject 100: Gantry 110: X-ray irradiation / detection apparatus 130: X-ray tube 132: Focus 134: X-ray 150: X-ray detector 152: X-ray incident surface 154: Detection cell 200: Table 202: Top plate 204: Cradle 206: Prop 208: Base 300: Operator console 302: Display

Claims (16)

An imaging unit that collects projection data of a subject by scanning using X-rays, and reconstructs tomographic images at a plurality of slice positions of the head based on the projection data;
Correction means for performing correction for reducing a false image in the tomographic image, generating correction data using bone projection data obtained by virtually projecting a bone image in the tomographic image, and reversing the correction data An X-ray CT apparatus having correction means including means for drawing a correction image projected and reconstructed from the tomographic image,
A gain that can be used to create the correction data to adjust the degree of correction is calculated based on the tomographic image of the head, and is applied to the inner region from the contour of the head cross section assumed to be circular. Gain setting means that is determined for each tomographic image at each slice position in accordance with the bone thickness that is the thickness of the bone in the circular radial direction when it is assumed that the bones included are uniformly present
An X-ray CT apparatus comprising: When the bone thickness is r, the area of the tomographic image of the head is S1, the area of the bone image is S2, and the radius of the head section assuming the circular shape is r1, the bone thickness is given by The X-ray CT apparatus according to claim 1, wherein the X-ray CT apparatus is calculated.
The gain setting means determines the gain so that the degree of correction by the correction data is greater when the bone thickness is smaller than when the bone thickness is large.
The X-ray CT apparatus according to claim 1. The gain maintains a gain value that is the first correction level in the range from 0 to the first bone thickness setting value, and exceeds the first bone thickness setting value to the second bone thickness setting value. In the range, the gain value is continuously changed from the gain value that is the first correction level to the smaller gain value that is the second correction level, and in the range exceeding the second bone thickness setting value, the second correction level Maintain a gain value of
The X-ray CT apparatus according to claim 3. Gain correction means for correcting the gain according to the area ratio of the bone image in the inner region that is more than k (> 1) times the bone thickness from the contour of the tomographic image with respect to the area of all bone images in the tomographic image
The X-ray CT apparatus according to claim 1, further comprising: The X-ray CT apparatus according to claim 5, wherein the correction is correction that reduces a degree of correction by the correction data. The X-ray CT apparatus according to claim 6, wherein the amount of correction is small when the area ratio is small and large when the area ratio is large. The correction amount maintains the first correction amount in the range from 0 to the first area ratio setting value, and the correction amount exceeds the first area ratio setting value and reaches the second area ratio setting value. It continuously changes from a correction amount of 1 to a second correction amount larger than that, and the second correction amount is maintained in a range exceeding the second area ratio setting value.
The X-ray CT apparatus according to claim 7. A correction method for reducing false images in tomograms at a plurality of slice positions of a head imaged using an X-ray CT apparatus, wherein a bone image in the tomogram of the head is virtually projected. A method of correcting the tomographic image including a step of creating correction data using the bone projection data to be obtained, and subtracting the corrected image reconstructed by backprojecting the correction data from the tomographic image,
A gain that can be used to create the correction data to adjust the degree of correction is calculated based on the tomographic image of the head, and is included in the inner region from the contour of the head section that is assumed to be circular. It is determined for each tomographic image at each slice position according to the bone thickness that is the thickness of the bone in the circular radial direction when it is assumed that there is a uniform bone.
An image correction method characterized by the above. When the bone thickness is r, the area of the tomographic image of the head is S1, the area of the bone image is S2, and the radius of the head section assuming the circular shape is r1, the bone thickness is given by The image correction method according to claim 9, wherein the image correction method is calculated.
The gain is determined so that the degree of correction by the correction data is greater when the bone thickness is smaller than when the bone thickness is large.
The image correction method according to claim 9. The gain maintains a gain value that is the first correction level in the range from 0 to the first bone thickness setting value, and exceeds the first bone thickness setting value to the second bone thickness setting value. In the range, the gain value is continuously changed from the gain value that is the first correction level to the smaller gain value that is the second correction level, and in the range exceeding the second bone thickness setting value, the second correction level Maintain a gain value of
The image correction method according to claim 10. The gain is corrected according to the area ratio of the bone image in the inner region that is more than k (> 1) times the bone thickness from the contour of the tomographic image with respect to the area of all bone images in the tomographic image.
The image correction method according to claim 9 or 10, wherein: The image correction method according to claim 12, wherein the correction is a correction that reduces a degree of correction by the correction data. The image correction method according to claim 14, wherein the amount of correction is small when the area ratio is small and large when the area ratio is large. The correction amount maintains the first correction amount in the range from 0 to the first area ratio setting value, and the correction amount exceeds the first area ratio setting value and reaches the second area ratio setting value. It continuously changes from a correction amount of 1 to a second correction amount larger than that, and the second correction amount is maintained in a range exceeding the second area ratio setting value.
The image correction method according to claim 15.